Having fought in the latter Italian Wars under Marshal Brissac he achieved prominence in court in 1569, when he was subject to the attentions of the acclaimed poet Ronsard.

In the civil war that followed he would command a company of infantry during the siege of La Rochelle, during which he received a severe wound to his arm in an assault.

Du Guast was granted a large monetary gift from the king in early 1575 and superseded Philippe Strozzi as commander of the French guard.

[1] Known for his roving romantic attentions, Du Guast started an affair with Françoise Babou de la Bourdaisière, wife of Antoine d'Estrées.

[3] This was the opinion of the contemporary historian de Thou, who charged Du Guast with a penchant for treating the high nobles of the court as his social inferiors.

[5] Du Guast was thus already among the entourage of Anjou in 1572, and as such participated alongside his lord in the execution of the kill lists, that would spiral out of control into the Massacre of Saint Bartholomew.

During one attempt on the bastion de l'Évangile which guarded the north approach to the city, Anjou reported to the king that Du Guast had been wounded.

Du Guast was among those favourites frustrated by the attentions bestowed upon Bellegarde, and competed with the future Marshal for the privilege of the position of 'Colonel-General of the Infantry'.

[10] Du Guast was also rewarded with the regiment of guard formerly commanded by Philippe Strozzi, he quickly reworked the composition of the company installing many other nobles who had accompanied Henri to the Commonwealth to replace the old leadership.

[17] It was Du Guast who had the responsibility of preventing Alençon's potential flight from court, a task in which he failed when the prince slipped out of the capital in September 1575.

[4] Several hours before Alençon snuck out of his quarters, du Guast having been informed that an attempt might be made by the prince, told the king that he should secure his brother in the Bastille.

In October the duke of Guise repelled the vanguard of a Protestant mercenary army that was attempting to enter France during the Battle of Dormans.

The Parisian diarist, whose work provides considerable information about Henri's favourites, L'Estoile, opined that he was murdered due to his contempt for Alençon.

Meanwhile the contemporary historian de Thou argued that he was killed due to having antagonised the great nobles of the court, by treating them as his social inferiors.